1. Field of the Invention
The present invention generally relates to utility programs for computers, and more particularly to a utility program for adapting a computer system to provide a backup drive that mirrors a primary drive, which is ready at all times to substitute in place of the primary drive in the event of failure of the primary drive.
2. Discussion of the Related Art
Since the introduction of the personal computer, personal computer technology has proliferated at an incredible pace. As personal computers grow in size, performance, and complexity, the need for a fast and dependable backup/restore mechanism also increases. There is, however, a general disparity in such computers between the medium used for primary programs and data--fixed hard disk drives--and that used for backing up those programs and data, generally magnetic tape drives, floppy disks, or removable hard disks.
As is known, a fixed hard disk drive is a random-access device having a read/write head that does not come into contact with the disk itself, but can seek data in any track and sector as it moves over the rotating disk. In contrast, a backup tape drive is a sequential access device having a head that is typically in continuous contact with the tape medium during seek, read, and write operations. Floppy disks, and removable hard disks, operate similarly to fixed hard disks, but suffer other shortcomings. Namely, floppy disks are usually smaller in capacity than fixed disks, and thereby require multiple units to back up one fixed disk. In addition, they are less reliable over time due to their portable design, which entails an inherently less rigid form of construction, as well as exposure to extremes of temperature, dust, moisture, and magnetic fields in the process of being removed, transported, and stored.
These disparities give rise to awkward adjustments when using one of these media to back up data from and restore data to a fixed disk drive. Generally, one has to locate and copy from data stored either in sequential order, or scattered over multiple units. At a minimum, one has to invest in frequent purchases of new backup media in order to guard against their reduced reliability. The consequence is that restoring a crashed disk, or even a single corrupted file, can involve considerable investment and down time on the part of the user.
With the increasing size of removable drives, it has become more feasible to use them to archive data. By way of terminology, however, an archival device is not the same as a backup device. A backup device is meant to serve as a stand-in, ready at a moment's notice to take over primary functions in the event of a main drive failure. To be useful, it must therefore be constantly updated to reflect the current state of the main system. In contrast, an archival device enables the long-term storage of data that will need only infrequent access in the future. It is written to once, and then put away for safekeeping.
No medium will best fulfill all the functions and objectives of a backup (in contrast to an archival) device for home and personal computers unless it is fungible, i.e., interchangeable with the primary medium. One example of an acceptable fungible medium is another fixed disk drive with a capacity that is either equal to, or greater than, the capacity of the primary drive(s).
This design objective, however, entails certain risks and difficulties, particularly in personal computers. To function most effectively as a backup disk, a fixed hard drive is connected as an integral part of the computer which it is designed to serve. At the same time, the backup fixed disk drive should not be accessible through the computer's normal operating system (and thus "visible" to a user) since erroneous accesses could corrupt the integrity of the files on the backup drive.
Another difficulty in providing a robust backup device relates to mirroring the operating system of the primary drive on the backup drive. Duplicating the operating system files themselves on a second fixed drive that is visible to that same operating system can also lead to random system crashes and irregularities. An important design objective of a backup device is that the backup disk itself must be easily converted into a primary unit if it becomes necessary to substitute it for the primary drive. By way of analogy, the problem is akin to designing a body with two hearts: the second heart must be ready at all times to take over the primary heart's functions with a minimum of hesitation or delay, but at the same time, it must not be allowed to interfere with the normal circulatory functions performed by the primary heart.
Prior art devices for both small and large computer systems have generally failed to address these specific issues. Because the cost of fixed storage capacity is a significant factor in small computer systems, the redundant arrays and multiple-drive concurrent backup systems designed in the past for large systems do not feasibly translate to desktop systems typically used by individuals in the office or at home. The backup systems designed in the past for desktop computers have either involved disparate (and hence non-fungible) backup media, or simultaneous writing of data to two hard drives that are both visible at all times to the operating system, with consequent problems and risks as noted above.
Accordingly, it is desired to provide a system and method that achieves both backup and restore functions for personal computers with a maximum of speed, efficiency and reliability. At the same time, it is desired to provide a system and method that is applicable to larger systems as well. In such larger system, a significant cost savings can be achieved because of the reduction in the number of backup disks needed, and the reduction in processing time devoted to backups.